Drain odours inside can suggest a dry trap, broken vent

https://learn.multnomah.edu/eportfolios/918/home/why-you-need-a-plumber-to-clear-blocked-drains

Drain odours inside can suggest a completely dry trap, split air vent, or partial clog; Geelong properties with huge trees or older drain lines may need CCTV inspections to find breaches and stop repeating smells.